This invention relates to storage batteries and in particular, the seals that are used to effect a fluid seal relationship between the battery terminals or posts and the battery case.
In a typical lead-acid storage battery, two battery posts are provided which extend through the battery case, usually through the cover portion. These posts extend from the anode and cathode battery plates. Each plate is constructed in a grid form, and the grid is filled with an active paste material. The electrolyte is usually a sulfuric acid mixture and the battery plate is constructed of a lead alloy such as lead-calcium.
Continuous charging of a lead-acid storage battery produces a gradual accumulation of a lead-oxide deposit within the anode grid. The specific volume of this oxide deposit is 21% greater than the specific volume of the lead alloy of which the plate is constructed. The gradual accumulation of this oxide therefore takes up more space in the grid which resultingly enlarges as the deposit forms. As a result of this enlargement, the plate increases in size and bulges at the edges, and the edges, which are straight in a new battery, become extremely curved. The most immediate consequence of this bulging is that the battery post is pushed upwards through the battery cover. This occurs simply because the post is connected to the upper edge of the anodes, which curves upward as the plate increases in size.
In a typical battery of this type a fluid seal is provided between the battery cover and the post to prevent leakage of the electrolyte from the interior of the battery container and seepage of the electrolyte up the battery post. In the prior art, one form of seal consists of simply an O-ring integrally disposed in the battery case around the battery post. In another type of arrangement, the post passes through a stuffing box that is integral with the cover. This stuffing box contains an O-ring and a gland which is screwed into the stuffing box for the purpose of squeezing the O-ring to achieve a secure seal between the stuffing box and the post. Representative examples of this apparatus are shown in U.S. Pat. No. 1,012,461 and U.S. Pat. No. 1,505,219.
These devices do not per se accommodate upward movement of the post through the battery case. This is because their ability to accommodate this movement is dependent entirely upon the frictional relationship between the post and the sealing apparatus. As the battery ages, however, this relationship changes because the post sustains some physical and dimensional changes. The most noticable change is a roughened surface and a slight increase in the post's diameter. As a result, the upward movement of the post through the seal of the battery is somewhat restricted. The result of this restriction is that the battery plate and the case are subjected to forces from the plate enlargement which would otherwise not be present if the post could easily move through the seal. These forces can crack the battery plate and also crack the case. Both can severely reduce battery life. Hence, while the prior art devices can provide an effective seal for a new battery, its is clear that they are subject to the effects from the change in post size that occurs with increasing battery age. Thus, they do not provide a post seal, which is effective throughout the battery's service life.